The system of the IEEE 802.16e that is undergoing international standardization with respect to broadband wireless access systems, does not have a layered architecture comprised of a HLR (Home Location Register), a VLR (Visitor Location Register), a MSC (Mobile Switching Center), a BSC (Base Station Controller), a RNC (Radio Network Controller), and the like, as in the existing 2G and 3G mobile communication systems, but instead, is comprised of only a MSS (Mobile Subscriber Station), a BS (Base Station) and a ASA (Authentication Service Authorization).
The broadband wireless access system defines the protocols of the MAC (Medium Access Control) layer and the PHY (PHYsical) layer that are common between the base station and the mobile station (MSS). FIG. 1 depicts an exemplary protocol layer architecture for a broadband wireless access system.
To minimize power consumption of a mobile station in a broadband wireless access system, a sleep mode is supported. A mobile station in sleep mode has a sleep period (duration) comprised of a listening window and a sleep window.
During the listening window, the mobile station receives from the base station, a broadcasting type traffic downlink message that indicates whether any downlink traffic is being transmitted thereto or that indicates whether ranging needs to be performed for maintaining uplink communication and for maintaining appropriate downlink coding type according to signal quality. During the sleep period, in order to save power, the mobile station receives only a minimal amount of downlink signals from the base station, and during this period, the mobile station performs scanning of neighbor base stations for handover and performs ranging in order to maintain uplink communication and maintain appropriate downlink coding type according to signal quality.
The sleep mode can be divided into three power saving class groups having common characteristics: Type 1, Type 2, Type 3. Examples of messages used to support sleep mode are as follows:
The sleep request message (MOB_SLP_REQ) is delivered from the mobile station to the base station through a Basic CID (Connection Identifier), and is a message that defines the power saving class and requests its activation.
The sleep response message (MOB_SLP_RSP) is a message in response to the MOB_SLP_REQ message, and upon its receipt, the mobile station groups the connections of the power saving class and performs activation according to the request in the MOB_SLP_REQ message.
The traffic download message (MOB_TRF_IND) is only used in power saving class Type 1, and when a mobile station is in sleep mode, by sending information that indicates whether there is any downlink traffic to that mobile station, a mobile station having such traffic is allowed to terminate its sleep mode.
The ranging request message (RNG_REQ) is used to request an uplink/downlink channel descriptor that changes to be synchronized with the currently serving base station or to request frame number synchronization of the physical layer.
The ranging response message (RNG_RSP) is a message in response to the RNG_REQ message, and allows the base station and mobile station to maintain synchronization by providing values for periodic ranging.
FIG. 2 depicts an exemplary signal flow for a sleep mode operation (power saving class type 1) according to the related art.
In order to minimize its power consumption, the mobile station sends a sleep mode request message (MOB_SLP-REQ) to the base station. In response, the base station sends information about a sleep mode start frame, listening period, sleep period, etc. via a response message (MOB_SLP-RSP) to authorize a change into sleep mode. Upon receiving such authorization for sleep mode, the mobile station can then change into sleep mode at the appropriate frame that was allowed in the MOB_SLP-RSP message. During the sleep period, with the exception of some special situations, the mobile station does not send or receive any MAC PDUs with the base station. If there is downlink traffic for the mobile station in sleep mode state, the base station sends a traffic downlink message the that mobile station to wake it up from its sleep mode state and allow data reception during the listening period. When the listening period ends, the mobile station returns to its sleep mode state.
As explained above, in the related art, the messages used by the mobile station to support sleep mode that are transmitted and received with the base station are defined, but the operations actually related to sleep mode are not defined for the protocol stack (layers) within the mobile station and the protocol stack (layers) within the base station. Namely, there are no definitions for the primitives with respect to information transferred between the MAC layer and upper management entity via the NCMS (Network Control Management System), within the protocol stacks of the mobile station and the base station, respectively.